Turbocharger for internal combustion engine

ABSTRACT

A turbocharger for an internal combustion engine having a housing wall member located on an inner periphery of a metal compressor housing and facing a curved profile portion of the compressor impeller. The housing wall member is separately formed of a resin such as polyphenylene sulfide and integrally held and secured to the compressor housing.

This application is a division of application Ser. No. 08/771,147, filedDec. 20, 1996 now U.S. Pat. No. 5,785,493.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a turbocharger for an internalcombustion engine, and more particularly, to an improvement of acompressor housing thereof.

2. Description of the Related Art

A turbocharger for an internal combustion engine receives exhaust gasfrom an engine exhaust pipe, rotationally drives a turbine wheel in aturbine housing, compresses air within a compressor housing under theaction of rotation of compressor impellers arranged via a drive shaftintegrally formed with the turbine wheel, and supplies the compressedair to the engine. The compressor housing and the compressor impeller inthe turbocharger as described above are generally made of aluminum alloycastings.

An engine with a turbocharger is now demanded to have a superchargingeffect from a low-revolution region of the engine. In the turbocharger,making an outside diameter of a curved profile portion of the compressorimpeller and a gap formed between the profile portion and the inner wallsurface of the compressor housing corresponding thereto as small aspossible while improving a blade-shape of the compressor impeller isfavorable for improving efficiency of the compressor. However, the smallgap involves a risk that the curved profile portion of the compressorimpeller rotating at an extra-high velocity may come into contact withthe inner wall surface of the compressor housing due to slight shaftvibration, resulting in breakage of the impeller, or further indestruction of the drive shaft.

In a conventional turbocharger, therefore, it has been the usualpractice to provide a gap of from about 0.3 mm to 0.5 mm between theinner wall surface of the compressor housing and the curved profileportion of the compressor impeller.

Making the gap between the impeller and the housing as small as possibleby a thermal-spray coating provided in the housing is already known, forexample, for a gas turbine (as disclosed in JP-B2-50-690, JP-A-52-72335,and JP-A-52-85031). More recently, JP-B2-04-40559 proposes a method of,in a turbocharger for automobile, forming by thermal spray a resincoating comprising a mixture of soft metal and resin or graphite ontothe inner wall surface of a compressor housing as a means of making theabove gap small and preventing occurrence of a damage to the compressorimpeller even upon contact with the compressor impeller.

As a means of making the gap between the compressor impeller and thehousing in a turbocharger of an internal combustion engine small, andpreventing occurrence of a damage to the impeller even upon contact withthe compressor impeller, JP-A-06-307250 proposes a turbocharger in whicha wall member separately formed from a composite material comprising aresin such as PTFE (polytetrafluoroethylene) or a mixture of the resinand graphite or glass wool is attached onto a wall surface of at leastthe portion of the compressor housing wall surface corresponding to acurved profile portion of the compressor impeller.

In the conventional art, the presence of a necessary minimum gap Twithin a range of from 0.3 to 0.5 mm between the curved profile portionof the compressor impeller and the inner wall surface of the compressorhousing puts restriction on improvement of compressor efficiency.

A thermal spray coating technique recently proposed, on the other hand,while being effective for improving compressor efficiency, needs makinga consideration in productivity with respect to thermal spray equipment,capability to handle many different types of compressors and masking ofproducts, and thus the problem is that a product cost is higher.

Even when the thermal spray coating technique is replaced by a techniquefor improving compressor efficiency, in which a separately formed resinmember is attached to the wall surface and a gap between the compressorhousing inner wall surface and the curved profile portion of thecompressor impeller of a turbocharger is made small, it is important torotate the compressor impeller at extra-high velocity without damagingthe compressor impeller upon contact between the wall member and thecompressor impeller. That is, it is important, upon contact of thesemembers, to smoothly shave the compressor housing wall member withoutcausing any damage such as deformation or breakage to the compressorimpeller.

SUMMARY OF THE INVENTION

The present invention has an object to provide a turbocharger in whichthe wall surface member is made of a resin member excellent inmachinability for allowing contact with the compressor impeller inextra-high velocity rotation so as to minimize the gap between the innerwall surface and the curved profile portion of the compressor impeller,thereby improving compressor efficiency, as well as causing no risk ofdamage to the compressor impeller even upon contact of these members, bya low-cost technique excellent in productivity. In the presentinvention, furthermore, the material of the wall member is taken intoconsideration so that, even when the wall member is shaven by a contactwith the compressor impeller and the shaven chips reach the cylinder,there would be no bad effect on the engine cylinder.

In order to achieve the above object, the present invention ischaracterized in that a resin wall member which is located on an innerperiphery of a metal member of a compressor housing and iscorrespondingly to a curved profile portion of a compressor impeller ismade of PPS (polyphenylene sulfide). More specifically, the foregoingwall member is tightened and fixed by means of connecting bolts engagedwith screw holes formed in the foregoing compressor housing. Further, aslight gap defined by the inner periphery of the wall member and theshape of the curved profile portion in the outer periphery of thecompressor impeller is set so that the gap on the inlet side of thecompressor impeller is larger than that on the outlet side of thecompressor impeller.

In the present invention, furthermore, taking account of expansion ofthe wall member, the contact portion between the compressor housing andthe wall member is limited to only the attachment surface, and gaps areprovided between these members without the above contact portion.

In the present invention having the construction as described above, thewall member made of PPS resin or a composite material comprising amixture of PPS resin and graphite or glass wool provided correspondinglyto the curved profile portion of the compressor impeller is shaven awaywithout damaging the compressor impeller upon contact of the curvedprofile portion of the compressor impeller with the wall member attachedto the compressor housing, because the wall member is made of a materialsofter than that of the metal composing the compressor impeller.

The gap between the curved profile portion of the compressor impellerand the wall member provided correspondingly thereto can therefore beset to a value closer to zero than the value of the gap of from 0.3 mmto 0.5 mm required in the conventional art. Particularly duringextra-high velocity rotation of the compressor impeller, i.e., duringtemperature rise caused by adiabatic compression on the compressor side,the fore-going gap can be set to perfectly zero in consideration ofthermal expansion of the wall member. In the present invention, forexample, even upon occurrence of contact between the compressor impellerand the wall member attached to the compressor housing as a result ofshaft vibration, the wall member attached to the compressor housing isshaven in response to the extent of contact, thus maintaining the gap ofzero.

This means that the gap of from 0.3 mm to 0.5 mm existent between theinner wall of the compressor housing and the compressor impeller in theconventional art can be adjusted substantially to zero, thus resultingin an improved compressor efficiency.

The wall member attached to the compressor housing can be resin-formedin a mold or the like, and then incorporated in the compressor housing(metal member), and the wall member thus made of a resin can be shavenwith the compressor impeller during preliminary operation such as duringconfirmation of fluid performance. A similar result is available byincorporating a resin-formed wall member into the compressor housing(metal member), previously cutting the wall member so that the gapbecomes null upon thermal expansion in the actual operating state(during extra-high velocity operation), incorporating the compressorimpeller and rotationally driving the same. Further, the wall member maybe forcedly shaven with the compressor impeller during actual operationwithout previously applying cutting or other working.

Various methods are conceivable, taking account of productivity, forintegrally forming the wall member of the compressor housing and thecompressor housing (metal portion). For integration of a resin memberand the metal member, it is possible to attach the resin member to themetal member of the compressor housing with the use of a metal memberinsert mold or the like. A wall member made of a PPS resin excellent inheat resistance, oil resistance and chemical resistance can bescrew-connected directly with the compressor housing (metal member). Afurther improved productivity is available by achieving such aconstruction. In this case, it is desirable to provide a gap forallowing expansion of the wall member for portions other than thecontact surface of these members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating an embodiment of a turbochargerfor an internal combustion engine according to the present invention;

FIG. 2 is a partially enlarged view of the compressor A shown in FIG. 1;

FIG. 3 is a partially enlarged view of a portion P shown in FIG. 2; and

FIG. 4 is a reduced fragmentary view taken in 10 the direction of thearrow Q of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a sectional view illustrating a turbocharger for automobile,in which a portion A represents a compressor portion and B, a turbineportion.

Exhaust gas from an internal combustion engine for automobile isintroduced from an inlet 101 of a turbine housing into a scroll 102,flows from a larger cross-section toward a narrower cross-section, andis discharged from an outlet 103 into an exhaust pipe. At this point, aturbine impeller 2 is rotated at a high velocity (at least 100,000 rpm)under the effect of energy of exhaust gas.

A drive shaft 3 of this turbine is bearing-connected to a bearinghousing 110 through bearings 111 and 112.

The bearing housing 110 is further provided with a lubricant path 113for supplying lubricant to the bearings and a cooling water path 114 forcirculating cooling water for the engine to cool the turbocharger.

The turbine portion B is assembled by attaching a shroud 115 onto a sideof the bearing housing 110, then inserting the drive shaft 3 through thebearings 111 and 112, securing a turbine wheel 2 to an end of this driveshaft 3, and screw-fixing the same to the bearing housing 110 withscrews 116 so as to cover the outer side with a turbine housing 1.

Upon rotation of the drive shaft 3 by rotation of the turbine wheel 2, acompressor impeller 4 attached to the other end of the drive shaft 3rotates in the compressor housing 5, compresses air sucked from an inlet50 of the compressor housing 5 with the compressor impeller 4, anddischarges compressed air to a scroll 51, which is then pumped to anintake manifold of the internal combustion engine.

The compressor portion A is assembled by pressure-inserting a sleeve 510with a thrust metal 511 from the opposite turbine side of the driveshaft 3 into the drive shaft 3.

Then, a seal ring 513 is engaged with grooves provided on an end face ofthe bearing housing 110 on the opposite turbine side, and another sealring 514 is attached to the outer periphery of the sleeve 510. A sealplate 8 is then attached so as to come into contact with these rings.

Then, a compressor impeller 4 is inserted into the drive shaft 3, andthe drive shaft 3 and the compressor impeller 4 are secured with a screw41 at the tip of the drive shaft 3.

Finally, the compressor impeller 4 is covered from outside with thecompressor housing 5, engaged with a spigot 515 on the outer peripheryof the seal plate 8. A portion of the seal plate 8 composing this spigot515 and a flange 517 for attaching the compressor formed in the bearinghousing 110 are inserted and secured between an annular portion of thecompressor housing and a C-ring 516 attached in a groove formed on thecompressor housing 5.

Although the main body of the compressor housing 5 is made of aluminumalloy castings, a wall member 5b made of a resin is integrated with theportion facing the curved profile portion 4a of the compressor impeller4 after assembly. The wall member 5b is made by resin-forming of a PPS(polyphenylene sulfide) resin or a composite mixture of a PPS resin andgraphite or glass fiber softer than the compressor impeller 4.

The wall member 5b is directly connected and secured to the main body ofthe housing 5 with screw members 7 engaging with holes 6 provided on aflat annular surface 52 facing the seal plate 8 of the main body of thecompressor housing 5 on an annular surface 5d at right angles to thedrive shaft 3 of the compressor impeller 4.

Further, the wall member 5b comprises a cylinder portion 5e extending inparallel with the drive shaft 3, and a curved portion 5c connecting thecylinder portion 5e and the annular surface 5d.

FIG. 2 is a sectional view illustrating only the compressor housing 5.

FIG. 3 is an enlarged view of the portion D delimited with a one-pointchain line in FIG. 2.

FIG. 4 is another representation of FIG. 2 as viewed in the arrow Qdirection in a reduced scale.

The relationship between the compressor housing 5 and the peripheralmembers will be described further in detail below with reference tothese drawings.

A recess 5f is formed in the portion of the compressor housing 5, whichfaces the curved profile portion of the compressor impeller 4. Thisrecess 5f comprises an annular portion facing the seal plate 8 forreceiving the wall member 5b, a cylinder portion along the drive shaftand a portion having the curved surface portion connecting theseportions.

The wall member 5b attached to this recess 5f serves as the wall surfaceof the compressor housing 5 facing the curved profile 4a of a pluralityof compressor blades 4b forming the compressor impeller 4.

The compression efficiency of the compressor is higher according as agap T between the housing wall surface and the profile of the impelleris smaller. In this embodiment, this gap T is designed to becomesubstantially zero during usual operation by the use of thermalexpansion of the wall member 5b on the basis of the principle of thepresent invention.

For the wall member 5b, the size R₁ from the center to the insidediameter of the cylinder portion, the size R₂ to the outside diameterthereof, and the size R₃ to the center of the screw hole 7a aredetermined from a forming mold, thus determining the size L₂ between thecenter of the screw hole and the inside diameter of the cylinderportion.

The screw hole 7a is provided through the center of an accommodationrecess 5bg of the screw top 7b of the screws 7 provided on the samecircle periphery.

The wall member 5b is in contact only on the housing-side surface 5b₁₀of the annular surface on which the screw hole 7a is formed, and formsan attachment surface.

As shown in FIG. 4, gaps G₁ to G₄ are formed between the other wallsurfaces of the wall member attachment recess of the compressor housing5 and the corresponding wall member.

At the room temperature, the gap G₃ between the axial end face 5bl ofthe cylinder portion 5e of the wall member 5b and the wall surface 5b₂of the corresponding recess is set to about 300 to 400 μm, the gap G₁between the surface 5b₃ of the cylinder portion 5e of the wall member 5band the corresponding wall surface 5b₄, about 250 μm, the gap G₄ betweenthe surface 5b₅ of the curved portion 5c thereof and the correspondingwall surface 5b₆, 500 to 600 μm, and the gap G₂ between the outerperiphery edge 5b₇ of the annular surface portion 5d of the wall member5b and the corresponding wall surface 5b₈, 300 to 400 μm as in the gapG₃.

PPS has a thermal expansion coefficient of 2 to 7×10⁻⁵ (1 to 6×10⁻⁵ whenglass is contained). These values of gaps are therefore based on anextent of expansion at about the thermal deformation temperature of 250°C. so that the wall member 5b, even when expanding toward the housing 5,does not come into contact with the recess wall surface of the housing.Or, when the wall member comes into pressure contact with the recesswall surface of the housing as a result of expansion, the reactionthereof may cause cracks or rupture in the wall member 5b.

Because impact stress resulting from contact with the compressorimpeller 4b concentrates on the curved portion 5e of the wall member 5b,the thickness thereof is designed to become gradually larger from thecylinder portion 5e toward the annular surface 5d. That is, thethickness T₄ of the cylinder portion is larger than thickness T₂ of theannular surface portion.

The top 7b of the screw 7, designed to perfectly fit in theaccommodation recess 5bg, never projects to the surface facing the sealplate 8 of the compressor housing 5, so as not to cause resistance tothe flow of air therethrough.

The depth T₁ of the recess 5f and the thickness T₂ of the wall member 5bare designed to ensure sinking of the wall member 5b into the recess 5fby a depth within a range of from 100 to 200 μm at the room temperatureso that the seal plate 8 side end face 5g of the metal portion of thecompressor housing 5 and the seal plate 8 side end face of the annularsurface portion 5d of the wall member 5b become substantially flush uponordinary operation.

The screw 7 is designed to have a longitudinal length L₁ longer than thedistance T₃ between the end face of the seal plate 8 and the bottomsurface of the screw accommodation recess of the wall member 5b, so thatthe screw 7 does not come off the screw hole 7a even when it loosens.

Furthermore, even when the loosening screw 7 jumps out to the seal plate8 side to tilt on the impeller 4 side, the strong flow of air duringrotation of the impeller 4 pushes out the screw 7 which thus never comesinto contact with the impeller 4.

The surface of the wall member 5 facing the impeller may previously beshaven and then assembled so that the gap T from the impeller becomesnull as a result of thermal expansion at about the ordinary operatingtemperature. In this example, however, the impeller itself was providedwith the shaving function.

More specifically, it was designed so that the gap T between the surfaceof the wall member 5b and the compressor impeller 4 became null uponassembly, and the molded wall member 5b without any working wasincorporated into the compressor housing 5. A test similar to therotation test carried out without fail before assembly into theautomobile was conducted, and the surface of the wall member 5b wasshaven by means of the compressor impeller 4 into a desired shape.

In the rotation test, revolutions of the compressor impeller 4 wasincreased up to about 160,000 rpm on the maximum. cutting traces of from0.03 to 0.05 mm remained on the surface of the wall member 5b. Thecutting traces were shallower on the inlet side than on the outlet sideof the compressor. The results of some tests taking account ofmanufacturing errors of the individual parts suggested that a design tobring the initial gap T to zero caused cutting traces of from 0.05 to0.15 mm.

Another fact found in these tests is that the wall member 5b made of aresin thermally expands under the effect of temperature increase of thecompressor housing resulting from adiabatic compression of air duringcompressor operation. The foregoing cutting traces naturally includethose coming from this thermal expansion.

The design values of the wall members 5b were therefore modified intovalues taking account of the foregoing two points (non-uniformitybetween outlet and inlet sides and thermal expansion coefficient).

That is, the thermal expansion coefficient was calculated in ananticipation of temperature increase from the room temperature to 80°C., and design was made with a radius R₁ larger by a value correspondingto this expansion.

Design was made also so that the radius was smaller on the outlet sidethan on the inlet side of the compressor.

In this example, a slight gap T is produced between the surface of thewall member 5b and the compressor impeller 4, and this gap T wasslightly smaller on the outlet side than on the inlet side.

A similar rotation test carried out on the compressor of this exampleresulted in only a cutting trace of about 0.02 mm in a part on theoutlet side of the compressor exit.

The same compressor after this initial cutting was subjected to severalsimilar rotation tests, and no increase in cutting traces was observed.

The results of tests carried out on various materials of the wall member5b are shown in Table 1.

                                      TABLE 1    __________________________________________________________________________                  Material                          PPS                  PPS     Polyphenylene-                                        PBT                  Polyphenylene-                          sulfide                                 PTFE   Polybutylene                  sulfide Glass- Polytetrafluoro-                                        terephthalate    Item          No mixing                          reinforced                                 ethylent                                        No mixing    __________________________________________________________________________    Inter-         Machinability in                  ⊚                          ∘                                 X      Δ    ference         interference    with Damage to impeller                  No deformation,                          Worn   Deformed                                        Worn    impeller      no wear         Hardness (D785)                  90 ˜ 100                          90 ˜ 100                                 58     80 ˜ 90    Deforma-      ∘ (medium)                          ⊚ (little)                                 ∘                                        Δ (large)    tion at         Thermal deforma-                  250° C.                          250° C.                                 50° C.                                        220° C.    high tion temperature                  or over or over                                 or over                                        or over    tempera-         (Test method:    ture D785)         Continuous service                  210° C.                          210° C.                                 250° C.                                        140° C.         temperature                  or over or over                                 or over                                        or over         (Test method:         UL746B)         Linear expansion                  2 ˜ 7                          1 ˜ 6                                 10 ˜ 17                                        2 ˜ 5         coefficient × 10.sup.-5         (test method:         UL746B)    Over-all judgement                  ⊚                          ∘                                 X      Δ    __________________________________________________________________________

The turbocharger shown in Table 1 had previously been subjected to arotation test similar to that with a compressor having a wall member ofthe above-mentioned PPS and initially shaven, and was continuouslyoperated at a continuous service temperature shown in Table 1."Deformation at a high temperature" in Table 1 shows the result thereof.

The wall member made of PPS (no mixing) was shavable by the impellerbecause the material was relatively brittle, with no deformation norwear in the impeller. The thermal deformation temperature was at least250° C. or over, and the continuous operation at 210° C. did not give alarge amount of deformation.

When using a glass-reinforced PPS mixing PPS with graphite or glasswool, the linear expansion coefficient is reduced by 70 to 50%. Whilethe overall hardness was almost the same as in the PPS material, therewas observed a slight trace of wear on the impeller, attributable to thecontact between the mixture and the impeller. The amount of deformationupon temperature increase is led to a smaller value corresponding to thedecrease in the linear expansion coefficient, which is superior to thoseof the others.

This means that the gap T between the wall member and the impeller doesnot fluctuate much at all temperatures ranging from the room temperatureto high temperatures. Even when designing so as to achieve a gap T ofnull at high temperatures, the gap T does not widen so much atrelatively low temperatures, so that the compressor can be operated at ahigh efficiency.

When using PTFE (polytetrafluoroethylene), a very high viscosityresulted in production of chamfer, leading to a deformation of theimpeller.

Although polytetrafluoroethylene alone poses some difficulties inpractice, deposition of a hard PPS on the surface of a substrate made ofthis polytetrafluoroethylene gives a wall member provided withadvantages of the both materials. In this case, the impact alleviatingeffect of polytetrafluoroethylene can be expected.

When using a no-mixing material of PBT (polybutylene terephthalate), thedeformation temperature is low, resulting in serious deformation at hightemperatures, and the long period of time of contact between theimpeller and the wall caused wear of the impeller.

However, if a mixed material suitable for this PBT is available, itwould show the same tendency as the glass-reinforced PPS, and can beused in practice.

The judging symbols ∘, x and Δ do not represent in or outside the scopeof the present invention, but shows easiness of practical application atthe present level of art for practical application, and a low ratingdoes not mean exclusion from the scope of the present invention.

It was confirmed that PPS had satisfactory affinity to engine lubricantand gasoline, and shaven chips, if coming into cylinders, did not exertany adverse effect on the engine.

Damage to the wall member caused by deviated contact or strongtightening of the screw 7 was prevented by placing a plain washer 10between the screw member 7 and the bottom surface of the screwaccommodation recess.

The gaps provided at portions other than the attachment portion of thewall member 5b served also to adjust expansion deformation of the wallmember 5b toward the impeller into an appropriate amount. Without thesegaps, all expansion toward the metal housing would appear on theimpeller side. In addition, this may cause deformation of, or damage to,the wall member itself.

Furthermore, as shown in FIG. 4, the wall member is secured in the axialdirection by three screws.

Since this limits axial thermal deformation to an amount correspondingto thickness T₁ of the wall member made of a resin, there is only aslight amount of deformation.

In the radial direction, on the other hand, a thermal deformationcorresponding to the size L₂ of the resin wall member with the securingscrew as reference, is led to a larger amount of deformation as comparedwith that in the axial direction.

To avoid this inconvenience, imbalance in the amount of deformation isabsorbed by making the gap between the resin wall member and thecompressor impeller larger for the radial direction G₁₁ than that forthe axial direction G₁₀.

Because performance of a compressor mainly depends upon the gap in theaxial direction, possibility to reduce the clearance in the axialdirection is favorable for achieving higher performance.

According to the present invention, as described above, the surface ofthe compressor housing facing the impeller is formed into a separatepiece from a PPS resin, which is assembled into the housing, and the gapbetween the two members is brought substantially to zero by the use ofthermal expansion of the resin in ordinary operation.

Because of these features of the invention, a turbocharger of aninternal combustion engine provided with a compressor having a highefficiency is available by a relatively simple process.

More specifically, the features are as follows. Portions other than theattachment surface of the wall member can be arranged with a gap so asnot to come into contact with the compressor housing itself. Thispermits elimination of excessive deformation, crack or breakage causedby thermal expansion.

Provision of a stopper for attachment screw permits prevention of damageto the engine caused by falling of a screw.

What is claimed is:
 1. A turbocharger for an internal combustion enginein which a separately formed wall member is attached to at least aportion of the compressor housing wall facing a curved profile portionof a compressor impeller, wherein the material for said wall membercomprises polyphenylene sulfide resin, wherein said wall member made ofa resin is held and secured by means of connecting bolts which engagewith screw holes formed in said compressor housing.
 2. A turbochargerfor an internal combustion engine according to claim 1, wherein thescrew securing portion of said compressor housing and the wall member isformed at a portion located further outside a maximum outside diameterof said compressor impeller.
 3. A turbocharger for an internalcombustion engine according to claim 2, wherein the annular surface ofsaid wall member is attached to said compressor housing in closecontact, and a peripheral edge of this annular portion faces to a partof the wall of the recess in said compressor housing with a gaptherebetween.
 4. A turbocharger for an internal combustion engine inwhich a separately formed wall member is attached to at least a portionof the compressor housing wall facing a curved profile portion of acompressor impeller, wherein the material for said wall member comprisesPolyphenylene sulfide resin, wherein a slight gap between the innerperipheral surface of said wall member made of a resin and the curvedprofile portion of the outer periphery of said compressor impeller isset so that a gap on said compressor impeller inlet side is larger thanthat on said compressor impeller outlet side at the room temperature. 5.A turbocharger for an internal combustion engine according to claim 4,wherein the length of said screw member is set to a value with whichsaid screw member coming off the screw hole of said wall member comesinto contact with a corresponding seal plate of the compressor.
 6. Aturbocharger for an internal combustion engine according to claim 5,wherein a slight gap between the inner peripheral surface of said wallmember made of a resin and the curved profile portion of the outerperiphery of said compressor impeller is set so that a gap on saidcompressor impeller inlet side is larger than that on said compressorimpeller outlet side at the room temperature.
 7. A turbocharger for aninternal combustion engine in which a separately formed wall member isattached to at least a portion of the compressor housing wall facing acurved profile portion of a compressor impeller, wherein the materialfor said wall member comprises polyphenylene sulfide resin, wherein anannular surface of said wall member forms an attachment surface in closecontact with said compressor housing.
 8. A turbocharger for an internalcombustion engine in which a separately formed wall member is attachedto at least a portion of the compressor housing wall facing a curvedprofile portion of a compressor impeller, wherein the material for saidwall member comprises polyphenylene sulfide resin, wherein an annularsurface of said wall member is attached to said compressor housing inclose contact, and a peripheral edge of this annular portion faces to apart of the wall of the recess in said compressor housing with a gaptherebetween.